'I talked Bell through key paper on RHI cost controls'

With the RHI scheme's budget badly running out of control in the summer of 2015, civil servants at DETI were working on ways to rein it in and outlined their plan in a submission that was written for Mr Bell on 8 July.

Mr Cairns had been told at in the second week of June that the plan was urgent but it took a full month for it to be put into writing for the minister.

Getty ImagesCopyright: Getty Images

It stated that the expected spend on the scheme would exceed the budget set aside for it and attributed that to a large number of poultry farmers signing up.

Mr Cairns says he can't remember giving Mr Bell a copy of the paper but he told him about it twice in July and on the first occasion - the day after it was published - he sat beside him, taking him through the detail.

'Working for Bell was like purgatory'

That caused the adviser "stress heaped upon stress" and he was subsequently signed off work by a doctor.

He claims he was invited by Mr Johnston to a clear-the-air meeting with Mr Bell and says that during a phonecall about it Mr Johnston gave him two options - reconcile with the minister or lose his job.

RHI InquiryCopyright: RHI Inquiry

He tells the inquiry that the situation was "exceptionally upsetting" and is "still upsetting to talk about".

Asked if he thought about not going back to his adviser role, he replies: "I guess we've got mortgages to pay and bills to pay and... life."

After discussing it with his wife he decided that going back would be "purgatory" but with a Northern Ireland Assembly election on the horizon the next spring "this too shall pass".

'I expected to be moved from Bell adviser role'

Mr Cairns says that when he returned to Belfast after the London incidents he fully expected to be removed as Mr Bell's adviser and that he'd be moved to work for another minister or to a role in the DUP.

RHI InquiryCopyright: RHI Inquiry

Inquiry barrister Mr Lunny (above) presses the witness a number of times about whether the reason he remained in his post was because the minister concerned was Mr Bell.

"That's probably a fair assertion," he says, adding that senior DUP adviser Timothy Johnston phoned Mr Bell to tell the minister that Mr Cairns would not be sacked.

'Foster was exceptionally popular and Bell felt that'

On a trip to London on 9 June 2015, Mr Cairns and Mr Bell went for dinner in an Indian restaurant, durig which the adviser put it to the minister that they could meet Arlene Foster and her adviser to discuss DETI matters as they had considerable experience in the department.

"Mr Bell was very much of the opinion that these issues would be under his control and there wouldn't be any input from minister Foster or Dr Crawford," says the witness.

Getty ImagesCopyright: Getty Images

He says he closed the conversation down when Mr Bell became "somewhat heated" as he didn't want it to become "unsavoury".

Giving the inquiry his interpretation of his minister's concerns, he says that it was "fairly clear that minister Foster had been exceptionally popular inside DETI and outside DETI" and that Mr Bell was "feeling that".

'Foster and adviser claimed they didn't know of RHI problems'

Arlene Foster and her adviser Dr Andrew Crawford claimed they knew nothing about problems with the RHI scheme during a meeting on 8 June 2015, says Mr Cairns.

He claims he met them briefly straight after the meeting he'd been involved in with the DETI minister and his officials on the same day, during which civil servants said the initiative was facing budget issues.

PACopyright: PA

Both Mrs Foster and her adviser had moved from the department running the scheme to the finance department a few weeks earlier.

Mr Cairns tells the inquiry: "They said: 'This is the firs we've heard about that', and I said: 'I'll keep you updated'."

Mrs Foster says in her evidence that the meeting happened at the end of June, while Dr Crawford can't remember it - Mr Cairns is adamant that it happened on 8 June.

'Bell sat passively at ministerial meetings'

Mr Cairns says he believes he first became aware that RHI was over budget at a meeting on 8 June 2015 attended by himself, the enterprise minister Mr Bell and senior DETI officials.

RHI InquiryCopyright: RHI Inquiry

DETI's deputy permanent secretary Chris Stewart emailed a colleague after the meeting, stating that Mr Bell had asked to be kept informed about a number of issues about the RHI, including legislation on changes to the subsidies it offered.

Asked if he can remember the minister's contribution to the meeting Mr Cairns says: "Jonathan would have sat quite passively while these discussions were happening."